The inventive concept relates to semiconductor memory devices, and more particularly, to semiconductor memory devices for reducing ripple noise of back-bias voltage, and methods of driving the semiconductor memory devices.
Reduction in leakage current of a semiconductor memory device such as a dynamic random access memory (DRAM) is an important issue. Leakage current generated in a DRAM causes refresh time of a memory cell to be reduced. An example of leakage current is junction leakage current or sub-threshold current. Junction leakage current is generated due to, for example, defects of a junction of a cell transistor, and sub-threshold current is a channel leakage current flowing through a cell transistor.
Junction leakage current can be reduced by reducing ion concentration in a channel. However, by reducing ion concentration in a channel, the sub-threshold current is increased. Sub-threshold current can be reduced by increasing a threshold voltage of a cell transistor. However, by increasing threshold voltage of a cell transistor, the junction leakage current is increased.
In order to simultaneously reduce the junction leakage current and the sub-threshold current, a negative-biased word line structure is used. In a semiconductor memory device including the negative-biased word line structure, a negative voltage is applied to non-selected word lines.